Okay so I used my summon pack pony spell, and it doesn't show up. I have cancelled, and reused the spell over and over. I have logged in and out, nothing. Any ideas on how to make him show up/become visible again?
Try /pet hide. You may have accidentally hidden him and that will toggle it off. You will probably also have to you re-hide your other pets afterwards.
Yeah, you need to be careful with that /pet hide command, because it is just a toggle and will hide what is currently visible AND unhide anything that is currently hidden at the same time. It is often better to right click the pet you want to hide and click the icon there to hide it.